As has already been said, if she can't accept your passion, then she isn't worth your time. That's basically just the surface of a much larger underlying issue, in that she's basically an attention whore (which can be expected with any young person, boys included, as we all think the world should revolve around us at that age) that expects you to do what she wants you to do, when she wants you to do it. It goes both ways, and that's anything but a reliable relationship.
My girl doesn't know **** about automotive mechanics. That said, I take the time to explain it to her, and even include her in wrenching, though she admittedly gets bored with it at times. Still, I patiently explain everything to her. What I'm doing, why I'm doing it, and what the ultimate outcome is once it's done. This helps her better understand why, and better understand my hobby and passion. For the record, she has never once complained about me spending time, or money on my Jeep. If anything, she asks me when I plan to do it next, so she can help out. Sort of funny how that works, but yea. When you find one worth your while, just be patient, and be thorough. The end result is well worth the effort.
Also, the aforementioned bus arrival analogy that I failed to quote..... spot on